Process of concentrating mixed-sulphide ores



Patented July 24, 1928.

UNITED STATES PATENT OFFICE.

PROCESS OF CONCENTBATING MIXED-SULPHIDE ORES.

ll'o Drawing.

This invention relates to an improvement inthe art of concentrating the values in ores by froth flotation, and in particular to the treatment of ores containing mixed sul- I phides such as copper and copper-iron sulphides with iron sulphides, or sulphides of other metals together with iron sulphides;

The invention has for an object the preferential flotation of cop er sulphides while l retarding the flotation o the iron sulphides,

and consists in introducing into an alkaline pulp small amounts of an acid sulphite or other compound tending to liberate the sulphite radicle and hydrogen irons in the pulp under the conditions obtaining in the flotation process.

It has heretofore been proposed to add sulphurous acid to an acidulated pulp comprising a mixture of sulphides of lead, zinc 2 and iron for the purpose of controlling certain other factors, but, so far as I am aware, neither sulphurous acid nor acid sulphites have. been used for the purpose of re'ecting iron sulphides while preferentially oating 2 other sulphides. It has also been proposed to employ normal sulphites for the lpurpose of retarding the flotation of zinc sulp ides in effecting the separation of lead and .zinc sulphides. However, I have found that in treating ores containing copper and iron sulphides the normal sulphites have only a slight depressing or retarding action on the flotation of the iron sulphides. On the other hand, I have found that when an acid sulphite is introduced into an alkaline pulp a very marked rejection of iron sulphides is shown.

I am unable to state positively why the acid sulphites should be so markedly superior in their effectiveness to the normal sulphites. I appreciate that when an acid sulphite is introduced into an alkaline pulp, reactive constitutents. are present that tend toward the conversion of the acid sulphite into the normal sulphite. However, without intending to be bound by any particular theory advanced, I believe that the difference in results obtained may be due to the Application filed June 30,

1927. Serial No. 202,744.

fact that in all chemical reactions a time factor is involved, and that, therefore, the acid sul hites act upon the iron sulphides before t e alkali present in the pulp has had time to bring about the conversion of the acid sulphites to the normal sulphites.

In carrying out my invention, lime, caustic soda or other alkali is added to the ore pulp, either before grinding in the ball mill or after grinding, until the water of the pulp is faintly or even decidedly alkaline to phenolph'thalein. To this pulp is then added a solution of sulphur dioxide in water, or a solution of a bisulphite such as ammonium, calcium, sodium or potassium bisulphite. The pulp is then immediately introduced into the flotation machine where suitable frothing and selective agents are added.

The amount of bisulphite or other similar com ound used may vary somewhat, depen ing upon the nature of the ore being treated, and the proportion that will bring about optimum results may be determined by preliminary tests with samples of the particular ore pulp that is to be treated. However, for an ore containing copper sulphides, iron sulphides and mixedcopperiron sulphides and assaying .978% copper and 2.45% iron, about one pound of bisulphite per ton of dry ore will produce very satisfactory results.

For purposes of illustration, I give in detail the results of practice with a process and apparatus of the mechanical agitation type, using ore obtained from the mines of the Utah Copper Company and containing sulphides of copper, copper and iron, and iron. The ore was ground with burned lime and predetermined quantities were weighed out and introduced into a J anney flotation machine, together with sufficient water to form a pulp of the desired consistency. Aqueous solutions of the normal sulphites and of the acid sulphites, together with reconstructed cresylic acid, were added. The reconstructed cresylic acid used was a. combined frother and selector prepared. as described in U. S. Patent No. 1,593,232. It will be understood, however, that other frothers or combined frothers and selectors may be used without departing from the invention. The test results are as follows:

Assays Selective agent Rougher tailing Per cent recovery Pounds Per cent Per cent Kind per ton Cu Fe Copper Iron None 082 0. 92 93. 25 69. 74 CaSO; 1. 0 085 1. 03 92. 19 61. 04 K280; 1. 0 080 1. 33 92. 41 49. 64 NazSOa 1. 0 082 1.45 92. 33 45. 93 (NH4)2SO;.--.. 1.0 .083 1.00 92.18 02.30

OaH:(SO3)2 1. 0 092 1. 92 91. 13 25. 66 KHSO; 1. 0 083 1. 62 92. 07 38. 11 NaHSOa 1. 0 082 1. 67 92. 24 d6. 82 NH4HSO3. 1.0 .088 1.83 91.48 28.80

The results here shown are the average of three days laboratory testing on differentheading samples.

In columns 2 and 3 are shown the results as to residual copper and iron contents of assays of the rougher tailing from'flotation with the various selective agents indicated, whereas in columns 4 and 5 are shown the recoveries of copper and iron in the concentrate collected in terms of percentages of the amounts of copper and iron originally present in the particular ore treated.

The tailing water from these tests, when titrated with tenth normal acid and phenolphthalein indicator, gave an alkalinity equivalent to about .040 pounds free CaO per ton of water. Four-tenths of a pound of the reconstructed ores lic acid per ton of dry ore was used in eac case. A solution of sulphurous acid will produce about the same effect, but solutions of sulphur dioxide in water are unstable unless very low concentrations are used and, therefore, are diflicult and disagreeable to handle.

These tests show that the acid sulphites cause a great deal more iron to be rejected into the tailing than the normal sulphites, without any appreciable increase in copper loss. The ore used for these tests assayed .978% copper and 2.45% iron. The rejection of iron showed by the acid sulphites over the normal sulphites or cresylic acid alone would mean an increase of 5% to 10% copper in the assay of the finished concentrate.

While the invention has been described with particular reference to its applicability in the treatment of copper sulphide ores, it will be understood that it may be applied to the separation of other valuable metal sulphides from their ores containing iron sulphides Where, as in the case of copper and iron sulphides, the valuable metal sulphide will float preferentially to iron sulphide under the influence of a bisulphite when such ore is in the form of an alkaline pulp.

I claim:

.1. The method of effecting the selective froth flotation of copper sulphides from ores containing iron sulphides, which comprises rendering the ore pulp alkaline, adding a substance capable of liberating sulphite radicle and hydrogen ions under the conditions obtaining in the flotation process, and sub jecting the resulting pulp to a flotation operation.

2. The method of effecting the selective froth flotation'of copper sulphides from ores containing iron sulphides, which comprises rendering the ore pulp alkaline, adding a small amount of an acid sulphite to said pulp, and subjecting the resulting pulp to a flotation operation.

3. The method of effecting the selective froth flotation of sulphide minerals, which comprises rendering ore pulp alkaline, adding a small amount of ammonium bisulphite to said pulp, and subjecting the said pulp to a flotation operation.

4. The method of effecting the selective froth flotation of copper sulphides from ores containing iron sulphides, which comprises rendering the ore pulp alkaline, adding a small amount of ammonium bisulphite to said pulp, and subjecting the said pulp to a flotation operation.

In testimony whereof, I have signed my name to this specification this 24th day of June, 1927.

HAROLD S. MARTIN. 

